As is known in the art and shown in the prior art system of FIG. 1, an airborne radar warning receiver (RWR) system on an aircraft 102, for example, indicates the direction of a radar 101 that illuminates the aircraft, alerting the crew to possible danger. For full circle protection, four antennas desirably are aimed (or boresighted) at an even angle spacing of 90 degrees. Emitter direction is determined by comparing signals from two antennas 103a,c with the strongest signals, which vary with antenna off-boresight angle in a known manner.
As the direction of arrival increases away from the antenna boresight direction, antenna gain decreases in a predictable manner. The signal strengths depend on antenna gain alone, since both antennas are essentially equidistant from the emitter, and receive energy at the same emitter beam angle. However, this ideal uniformity at times is not met, since RWR antenna gain is disturbed by reflections and shadowing from the aircraft that can cause significant errors.